The present invention relates, in general, to electronic circuit assemblies, and more particularly to electronic circuit assemblies having improved heatsinking capabilities.
Modern electronic circuit assemblies include high power analog and digital semiconductor devices which inherently generate a great deal of heat. The heat generated by the components must be dissipated during operation in order to maintain acceptable operation temperatures.
Conventionally, electronic components are mounted on printed circuit boards. Printed circuit boards are not good heatsinks, but provide the electrical insulation necessary for electronic circuit operation, and provide a substrate for printed circuits connecting the various components. In order to dissipate heat, the conventional printed circuit boards are typically mounted on metal, e.g. copper, heatsinks which will draw the heat from the circuit board.
In analog electronics, as frequencies and power increase as required by modern telecommunications for example, the above described heatsinking arrangement is not sufficient to maintain operable temperatures. The same problem arises in digital electronics for example with high performance microprocessors. A prior art solution is to isolate the particular components generating the most heat, and attach them separately to the metal heatsink which lies below the printed circuit board. This is accomplished by providing an opening through the printed circuit board, the opening accessing the metal heatsink.
The heat generating component can not be attached directly to the metal heatsink because it must be attached to an electrically insulating substrate. Consequently, the heat generating component is first attached to a ceramic substrate. The ceramic substrate is then attached to the metal heatsink, through the opening in the printed circuit board.
The prior art solution gives rise to particular disadvantages. For example, the ceramic substrate between the heat generating component and the heatsink does not dissipate heat particularly well. Ceramics have approximately 1/100 the heat dissipation ability compared to copper. Consequently, although operable temperatures can be maintained, there will be localized heat gradients, the heat being high near the heat generating component mounted on the ceramic substrate. This leads to problems such as metal migration, which eventually results in device failure.
Additionally, beryllium oxide is typically used as the ceramic substrate because it has fairly good heat dissipating characteristics. However, beryllium oxide gives rise to toxic substances during processing. Furthermore, since the ceramic connecting the heat generating component through the heatsink is not a particularly good heat dissipater, the electronic component itself must be designed to dissipate heat as efficiently as possible. Typically, the electronic component is a semiconductor die. In order to provide efficient heat dissipation, the semiconductor die is often thinned to as little as 5 mils. The thinning leads to a more fragile device and requires extra processing, and therefore negatively impacts cost and yield.
What is needed is an electronic circuit assembly with improved heatsinking which overcomes the disadvantages of the prior art. Specifically, a heatsinking arrangement is needed which conducts heat efficiently and uniformly, while providing electrical insulation without the need for an extra ceramic substrate. Additionally, it would be desirable to provide enough heat dissipation so that the heat generating component does not need to be thinned.